A) as a heat source id recommend a heating pad, you can pick them up at any large chain petstore, or the cheaper route is to order online.
B) youll also need substrate like you mentioned. aspen is ideal and affordable.
C) your snake will also need atleast 2 hides- one for the cooler side, and one for the warmer side. these can be bought at a petstore, ordered online, or made from things at home- a coolwhip/sour cream container, etc. just cut a tiny hole at the lip of the bowl for entry/exit.
D) you will need a thermometer and a hygrometer or a therm/hygro combo. you can find them at most pet stores, or online, and digital is always recommended. the little analog cheap dial ones can be up to 20 degrees off up or down, and the hygrometers are also way off. i recommend getting one that has the ability to measure both sides of your tank.
E) youll need a thermostant to regulate the temperature of the warm side of your tank to prevent wacky temp fluctuations, burns, and to maintain a consistent temp, etc.
F) and last but not least, youll need feeders. i recommend
www.laynelabs.com for ordering feeders, you can order in bulk like up to 1000, or as little as 25, which is handy if you dont have a lot fo snakes and dont want to pay for 100 mice minimum at once, which will most likely result in waste.
G) like you said a small waterbowl too, and i think thats all off the top of my head.
and i always recommend ordering online from somewhere like bigappleherp.com, petmountain, etc. its muchhhh cheaper than store bought supplies. hope this helps =] sorry so long! =p good luck